The hypothalamus and photoperiodic control of FSH secretion by melatonin in the male Syrian hamster

Bonnefond, C.; Walker, Alonzo P.; Stutz, Jan; Maywood, Elizabeth S.; Juss, TS; Herbert, J.; Hastings, Michael H.

doi:10.1677/joe.0.1220247

Cited by 42 publications

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“…The most frequently studied physiological response to the melatonin signal involves the photoperiodic control of reproductive activity, and this effect of melatonin is thought to be mediated via a hypothalamic site of action in rodents (16,20,21). Although, in the ovine brain, there is a wide distribution of melatonin binding sites within the hypothalamus, a recent study (22) has shown that, in Soay rams, intracranial melatonin implants are more effective when placed in the medial basal hypothalamus than in the preoptic area.…”

Section: Discussionmentioning

confidence: 99%

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Melatonin Binding Sites in the Ovine Brain and Pituitary: Characterization During the Oestrous Cycle

Heiliwell¹,

Williams²

1992

J Neuroendocrinology

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The distribution of putative melatonin receptors in the sheep has been investigated using in vitro autoradiography and the high affinity, high specific activity ligand 2-[(125) l]iodomelatonin. A wide distribution of specific labelling was found in both the ovine brain and pituitary gland as previously reported. Several novel areas of binding were also identified in the present study, including a fine layer of labelling at the medial edge of the diagonal band of Broca, the trigeminal nucleus, laminae II and III of the substantia gelatinosa, the molecular layer of the cerebellum as well as a scattered labelling in the pars distalis of the pituitary. There was no evidence of specific labelling in any of the peripheral tissues examined. Characterization studies performed on both neuronal and pituitary melatonin binding sites revealed that binding was time- and temperature-dependent and reversible on addition of 1 μM melatonin. The binding of 2-[(125) l]iodomelatonin was also competitively inhibited by increasing concentrations of 2-iodomelatonin and melatonin. The inhibition constants (K(i) ) estimated for each of these substances were similar for both neuronal and pituitary sites. Saturation studies also revealed similarities between neuronal and pituitary tissues with 2-[(125) l]iodomelatonin binding specifically to a single class of high affinity binding sites. Values for equilibrium constants (K(d) ) were within a range of 28 to 48 pM, and values were found to be not significantly different amongst the four regions of the brain investigated and the pars tuberalis of the pituitary. In contrast, the concentration of 2-[(125) l]iodomelatonin binding sites (B(max) ) ranged from 3 to 218fmol/mg protein and were maximal for the pars tuberalis. Saturation studies on brain and pituitary tissues taken from ewes killed either on the day of oestrus or during the luteal phase of the oestrous cycle, indicated that no differences exist in the affinity or concentration of 2-[(125) l]iodomelatonin binding in any region between the two times of the cycle investigated.

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Section: Discussionmentioning

confidence: 99%

“…hypothalamus/preoptic area (20,21). In the sheep, one study using melatonin implants in the highly seasonal Soay ram found them to be most effective when placed in the medial basal hypothalamus (22).…”

mentioning

confidence: 99%

Melatonin Binding Sites in the Ovine Brain and Pituitary: Characterization During the Oestrous Cycle

Heiliwell¹,

Williams²

1992

J Neuroendocrinology

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“…The decline a t the end of night is equally precipitous and as a result the pineal broadcasts what may be viewed as a square wave signal, the duration of the nocturnal melatonin peak varying in direct proportion to the length of the night (2-10) and with successive signals separated by daytime levels which are not significantly different from zero. By using programmed systemic infusions of melatonin to mimic this square wave pattern, it has been shown that the photoperiodic response of pinealectomized animals depends upon the duration of the nocturnal peak but not the phase of the light-dark cycle at which it is encountered (3,(11)(12)(13)(14)(15)(16)(17). A 10 h infusion of melatonin delivered once every 24 h for 5 to 6 weeks mimics short daylengths whereas a 4 h signal is read as a long day.…”

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confidence: 99%

Occlusion of the Melatonin‐Free Interval Blocks the Short Day Gonadal Response of the Male Syrian Hamster to Programmed Melatonin Infusions of Necessary Duration and Amplitude

Maywood

Lindsay

Karp

et al. 1991

J Neuroendocrinology

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Photoperiodic control of the neuroendocrine axis is mediated by changes in the duration of the nocturnal melatonin signal. This study tested the hypothesis that reading of the signal depends upon the presence of a period free of melatonin between successive signals. Adult male Syrian hamsters were pinealectomized and received chronic subcutaneous infusions of melatonin or saline for 6 weeks. Animals which received saline had large testes. Those which received a single daily infusion which lasted for 10 h (50 ng/h) followed by 14 h without infusion underwent gonadal atrophy. Other animals received a compound melatonin signal in which the melatonin-free interval was occluded by a continuous infusion (25 nglh). Superimposed upon this was a 10 h phasic increase in infusion rate such that the maximum rate of infusion was equivalent to that observed in controls (25 ng/h increase, 50 nglh peak rate), or the increase in rate over the baseline was the same as in controls (50 nglh increase, 75 nglh peak rate). In neither group did the animals undergo gonadal regression. Analysis of iodomelatonin binding sites by in vitro autoradiography failed to reveal any systematic difference between animals which did and did not respond to melatonin and so the absence of a response could not be attributed to loss of receptors. These data demonstrate that the photoperiodic system cannot identify the melatonin signal solely upon the features of nocturnal peak height or amplitude of the peak over baseline. They are consistent with the hypothesis that the melatonin-free interval plays a significant role in photoperiodic time measurement.

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“…As a result, melatonin reduces the release of LH and FSH (34)(35)(36). This may interfere with the pulsatile ability of GnRH, acting directly on the control of the synthesis of gonadotropins or dopamine, or acting indirectly on the PVN and the PVT (37,38).…”

Section: Discussionmentioning

confidence: 99%

Effects of melatonin on the ovarian response to pinealectomy or continuous light in female rats: similarity with polycystic ovary syndrome

Lima

Baracat

Simões

2004

Braz J Med Biol Res

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The current study was conducted to investigate the relationship between melatonin and chronic anovulation. Adult (3-4 months old) female Wistar rats were submitted to pinealectomy: group I: pinealectomized ovariectomized melatonin-treated (N = 10); group II: pinealectomized ovariectomized placebo-treated (N = 12); group III: pinealectomized light-treated placebo-treated (N = 10) or maintained under continuous light; group IV: maintained under continuous light, ovariectomized melatonin-treated (N = 22); group V: maintained under continuous light, ovariectomized placebo-treated (N = 10); group VI: maintained under continuous light placebo-treated (N = 10). In order to assess ovarian modifications, unilateral ovariectomy was performed during the fourth month in groups I, II, IV, V and the other ovary was removed after 8 months. Ovariectomy was performed in groups III and VI only after eight months. Melatonin (200 µg/100 g body weight) dissolved in 0.02 ml absolute ethanol was injected intramuscularly daily during the last 4 months into groups I and IV. The other groups were treated with placebo (NaCl). The ovarian cysts were analyzed and their area, perimeter and maximum diameter, as well as the thickness of the ovarian capsule were measured. Daily colpocytological smears were performed throughout the study. Persistent estrous condition and ovarian cysts were observed in all groups. In pinealectomized rats the ovarian and vaginal alterations disappeared at the end of the study and in rats maintained under continuous light the vaginal and ovarian polycystic aspect was reversed only in those treated with melatonin. We conclude that melatonin may act on the ovarian response reverting chronic anovulation induced by pinealectomy or continuous light.

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The hypothalamus and photoperiodic control of FSH secretion by melatonin in the male Syrian hamster

Cited by 42 publications

References 0 publications

Melatonin Binding Sites in the Ovine Brain and Pituitary: Characterization During the Oestrous Cycle

Melatonin Binding Sites in the Ovine Brain and Pituitary: Characterization During the Oestrous Cycle

Occlusion of the Melatonin‐Free Interval Blocks the Short Day Gonadal Response of the Male Syrian Hamster to Programmed Melatonin Infusions of Necessary Duration and Amplitude

Effects of melatonin on the ovarian response to pinealectomy or continuous light in female rats: similarity with polycystic ovary syndrome

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